Seattle has Microsoft. Boston has Harvard. San Jose is higher-tech, New York more cosmopolitan.

But the Washington region has something those cities do not: the best-educated population in the nation.

Almost half of adult Washington area residents have college diplomas, and better than one-fifth have graduate or professional degrees. By either measure, the region has the most educated population of any large metropolitan center.

To demographers, this was no revelation. The area has ranked as the country's best-educated metropolis for at least four decades. The suburbs of Bethesda and Arlington County occasionally surface on lists of smartest cities.

But the area as a whole is not particularly known for erudition. The "best-educated" claim is more readily identified with other places: Seattle; Boston, the nation's first college town; and collegiate state capitals such as Austin and Madison, Wis.

"When you think about, 'Where are the smartest workers?', you don't think of the federal agencies," said Alan Berube, a senior fellow and research director at Brookings who wrote part of the study, which was released in May. "You think of Microsoft, you think of Silicon Valley, you think of MIT."

Washington's smarts are subsumed by its deeper identity as the seat of federal government. That image overshadows many demographic traits that might define another city.

If there is some confusion over the identity of the best-educated city, that's partly a matter of how "city" is defined. The District, exclusive of its suburbs, isn't quite so well-educated as either Seattle or San Francisco. Even Bethesda can stake a claim as smartest city, if smaller jurisdictions are included in the list.

But as a metropolitan area -- city and suburbs -- Washington is without peer. The District is surrounded by the five best-educated counties in the country, as measured in bachelor's degrees, a necklace of demographic pearls: Arlington, home to the Pentagon; Alexandria, the upscale Colonial city, classified by the census as its own county; Fairfax County, headquarters of Sallie Mae and the CIA; Howard County, with its massive Johns Hopkins University Applied Physics Laboratory; and Montgomery County, home to the National Institutes of Health. There are Washington suburbs where seemingly every neighbor is a doctor or lawyer, scientist or spy.

"I remember when I was knocking on doors as a candidate: You get to talking to somebody and find out they're an expert in their field," said Howard County Executive Ken Ulman (D).

Urban neighborhoods teem with 20-somethings, fresh from graduate school and drawn to the quintessential white-collar city.